NEW YORK (CNN) -- New York celebrates the centennial of its most famous New Year's tradition Monday, as organizers of the Times Square ball drop have given the crystal globe an environmental makeover.

Technicians prepare the New York Times Square ball Thursday for the event's 100th anniversary.

This year the 1,415-pound ball has been outfitted with more than 9,500 energy-efficient light-emitting diodes that will illuminate the ball's more than 600 crystals. The LEDs will use the same amount of electricity as about 10 toasters, say event officials.

New York police estimate about a million people will crowd Times Square to watch the ball drop from a flagpole atop the One Times Square building at midnight.

Another billion people worldwide are expected to watch the spectacle on video, said Tom Chiodo, a spokesman for the Times Square Alliance. Of those viewers, 100 million will be in the United States, he said.

New York Mayor Michael Bloomberg will be joined by Iraq war veteran Karolina Wierzchowska, who was also a Ground Zero guard worker and a New York Police Academy valedictorian -- to push the button for the ball drop at 11:59 p.m.

Live from Times Square

Bring in the New Year with Anderson Cooper and special guest Kathy Griffin.Tonight at 11 p.m. ET

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Kelly said that once the Times Square attendees pass the entrance gates, they will not be able to leave.

New York's terrorist threat level remains at orange -- the nation's second highest level -- as it has since the September 11, 2001, attacks.

"We certainly haven't let our guard down," Kelly said.

As the ball drops, the new year will be greeted with a massive fireworks explosion, some 168 shots in the first five seconds alone, and a downpour of two tons of fireproof confetti. Some of the confetti includes New Year's wishes that were written by visitors to the city in nearly two dozen languages.

Over the past week, visitors from across the country wrote their messages on a Times Square "Wishing Wall."

"I want to turn the world green and the water clean," one person wrote.

"Let my husband stop snoring," another wrote, while others were more serious: "That my mom will get her kidney transplant" and "Peace in Pakistan."E-mail to a friend